1. Field of the Invention
This invention relates to a system for controlling the rate of fuel injection into an engine, such as a diesel engine.
2. Description of the Prior Art
In diesel engines, fuel is periodically injected into engine combustion chambers by means of fuel injection pumps. The quantity of fuel injected during each injection stroke is adjusted in accordance with operating conditions of the engines. Specifically, a movable control member or sleeve in the injection pump determining the fuel injection quantity is driven in response to the operating conditions of the engine.
It is known to adjust the position of the control member to a desired position dependent on the engine operating conditions by means of a feed-back control system. In this system, a position sensor monitors the actual position of the control member and generates a signal indicative thereof. On the basis of the difference between the actual position signal and a signal representing a desired position of the control member, an electrically-powered actuator drives the control member to adjust its actual position toward its desired position.
Even in this feed-back control system, at a fixed position of the control member, the fuel injection quantity in terms of mass varies as the fuel density changes. It should be noted that commercially available fuels for diesel engines have various densities. Also, the density of the fuel varies with its temperature. What is worse, in this system, the fuel injection quantity determined by the position of the control member varies as the sliding parts of the fuel injection pump wear away. Accordingly, the fuel injection quantity or rate in terms of mass does not have a constantly fixed relationship with the engine operating conditions. The relationship between the fuel injection quantity or rate in terms of mass and the engine operating conditions should be constantly fixed for reliable control of the engine.